1. Field of the Invention
Apparatuses consistent with the present invention relate to optoelectronics, and more particularly, a dynamic image regulator used in various apparatuses for optically recording and reproducing information.
2. Description of the Related Art
Various attempts have been known for solving a problem with controlling an optical radiation intensity by using various physical and chemical effects.
For example, there are documents regarding a radiation attenuator based on a nonlinear-optical effect known as light-reduced dissipation. Light-reduced dissipation is main mechanism in attenuators based on light-reduced diffraction gratings in crystals with impurity of transition metal ions (see RU Patent No. 2282880). An attenuation effect arises due to increase in light diffusion when radiation intensity is increased.
In addition, a liquid-crystal regulator for controlling radiation intensity has been known. In the liquid-crystal regulator, a liquid-crystal layer is disposed between transparent electrodes and two crossing polarizers (see Display Device, Ed. J. I. Pankove, Springer-Verlage, Berlin, 1980). When a driving signal is applied to the liquid-crystal layer, polarization twisting occurs, and the intensity of light passing through the liquid-crystal regulator varies.
A light intensity regulator based on linear electro-optical effect includes a crystal having electro-optical effect, or organic or inorganic film having electro-optical effect, and the crystal or the film is disposed between transparent electrodes and two crossing polarizers (see, e.g., W. Brunner, K. Junge, Wissensspeicher Lasertechnic, VEB Fachbuchverlag, Leipzig, 1987). When a driving electric signal is applied to the electro-optical crystal or film, the polarization twisting occurs, and the intensity of light passing through the liquid-crystal regulator varies.
A light intensity regulator based on a linear electrochromic effect includes a film formed of inorganic or organic electrochromic material and electrolyte. The film and the electrolyte are disposed between transparent electrodes (see, e.g., D. M. DeLongchamp, M. Kastantin, P. T. Hammond, Chem. Mater. 15. P.1575, 2003). When a driving electric signal is applied to the electrodes, a chemical composition of the film changes, and the transmissivity of the film varies.
Also, a light modulator based on total internal reflection distortion (TIRD) has been well known. Modulation mechanism of the light modulator is based on a thickness variation in a gap between two total internal reflection prisms, or on variation in refraction index of a layer disposed in the gap. This variations lead to change in conditions of tunneling an electromagnetic wave from a first prism into a second prism, and, as a result, to change in transmissivity and reflectivity of the light modulator. The light modulator based on TIRD can be used as a radiation attenuator driven by an external driving signal. A gap value between the prisms is changed, for example, by a piezoelectric mover (see, e.g., RU Patent No. 2022433, U.S. Pat. Nos. 5,555,327 and 5,841,916), or by magnetostriction elements (see, e.g., RU Published Patent Application No. 96103862).
The light modulator based on TIRD is advantageous in that light diffusion led to distort an image does not occur, design can be simplified, and temperature operation range is wide.
On the other hand, the light modulator based on TIRD is disadvantageous in that it is complicated to control the brightness and region of individual image point.
A light modulator based on reflective-type micro-opto-electro-mechanical systems (MOEMSs) has been known. Reflective-type MOEMSs are an array of micro-mirrors whose spatial arrangement is specified by an electrical signal (see, e.g., M. Hoffmann, E. Voges, Bulk silicon micromachining for MEMS in optical communication systems, J. Micromachin. Microeng., 12. 349. 2002, L. Y. Lin, E. L. Goldstein, R. W. Tkach. Free-space micromachined optical switches for optical networking, IEEE J. Sel. Top. Quant. Electr. (MOEMS), 5. 4. 1999.). Micro-mirrors are controlled by an electrostatic manner, piezo-mover or thermal actuator expansion or bending. For example, in U.S. Pat. No. 7,224,512, an element stopping an optical device at two or more locations by using an electrically-neutral limiter is used in order to move the optical device.
Reflective-type MOEMSs are advantageous in that the amplitude of spaced optical signals can be digitally controlled in telecommunication systems. However, reflective-type MOEMSs are disadvantageous in that only two states of each system element, i.e., an open state and a closed state are allowed and it is difficult smoothly modulate the amplitude of optical signals.